Method and system for supporting sparse explicit sounding by implicit data

ABSTRACT

A method and apparatus for an access point (AP) accessing a channel occupied by a neighboring AP within clear channel assessment (CCA) range. The method is implemented by setting a transmit null towards the neighboring AP, while acquiring accurate channel knowledge with minimal bandwidth penalty to surrounding networks, via a combination of sparse explicit sounding, and a following implicit channel estimation of the neighboring APs for updating the explicit data achieved by the sparse explicit sounding. An AP implementing the method is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/449,431 filed on Aug. 1, 2014, which claims the benefit ofU.S. Provisional Application No. 61/955,433 filed on Mar. 19, 2014. Thisapplication also claims the benefit of U.S. Provisional Application No.61/955,433 filed on Mar. 19, 2014 and U.S. Provisional Application No.61/971,200 filed on Mar. 27, 2014. All of the above applications areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to wireless communication, andmore specifically to high efficiency Wi-Fi transmissions.

BACKGROUND OF THE INVENTION

Prior to setting forth the background of the invention, it may behelpful to set forth definitions of certain terms that will be usedhereinafter.

The term “Wi-Fi” as used herein is defined as any wireless local areanetwork (WLAN) products that are based on the Institute of Electricaland Electronics Engineers (IEEE) 802.11 standards.

The term “Access Point” or “AP” as used herein is defined as a devicethat allows wireless devices (also known as User Equipment or “UE”) toconnect to a wired network using Wi-Fi, or related standards. The APusually connects to a router (via a wired network) as a standalonedevice, but it can also be an integral component of the router itself.

The term “client” as used herein is defined as any device that haswireless communication capabilities, specifically, the IEEE 802.11standards. A client may be for example a smart telephone, a laptop, atablet or a personal computer (PC).

The notation “STA” as used herein is defined in as an IEEE 802.11client.

The term “BSS” is an acronym for Basic Service Set, which is typically acluster of stations supported by an AP.

The term “node” as used herein is defined as general name for both IEEE802.11 AP and IEEE 802.11 STA.

The term “serving AP” as used herein is defined in relation to one APand one STA, wherein the STA is registered to the AP, and the AP and STAare sending and receiving data to and from each other.

The term “neighboring APs” or “neighboring nodes” relate to twoco-frequency (or co-channel) APs or nodes that are within each other'ssensitivity range, e.g. at least one of them can receive the other insuch an signal-to-noise ratio to allows decoding of signals.

The term “CCA range” as used herein is a range between two IEEE 802.11nodes, wherein at least one node can receive the other's transmission ata power level equal or larger than “CCA Level” e.g. −82 dBm.

The term “CSMA/CA” stands forCarrier-Sense-Multiple-Access/Collision-Avoidance, representing arequirement to listen before transmitting in a multi-node wirelesssystem that shares a common channel on the basis offirst-come-first-served.

The term “preamble” as used herein describes a certain 802.11transmitted signal modulation appearing at the beginning of each packet,that when received by other 802.11 nodes, will force them to yieldchannel access.

The notation “SINR” stands for Signal to Interference plus Noise Ratio.

The term “ACK” as used herein, stands for acknowledgement, and isdefined as the signal transmitted from an IEEE 802.11 receiving node tothe IEEE 802.11 node that has transmitted a packet to it, provided thepacket was successfully received.

The term “time division duplex” (TDD) as used herein refers to systemsusing the same frequency spectrum for methods of communications in atime division manner such as Wi-Fi systems.

The term “channel sounding” or simply “sounding” is the process definedin 802.11 specifications that enables the full dimensionality of theradio channel to be determined. One sounding technique described in the802.11 specifications is for an AP to transmit a Null Data Packet (NDP),a packet without a MAC frame.

The term “implicit channel sounding procedure” or simply “implicitsounding” is the process defined in 802.11 specifications, where bothdown and up links share the same spectrum. In the aforementionedprocess, the uplink channel estimated by the AP, is assumed to beidentical to the downlink one—based on reciprocity principle—and istherefore is considered by the AP to represent the channel towards theclient/STA. Specifically, an AP sends a request for a standard (known)sounding packet to the STA. In response, the STA sends the soundingpacket and the AP estimates the uplink channel. The downlink channel isthen assumed to be identical. As channel reciprocity is assumed, acalibration process is mandatory in implicit sounding.

The term “explicit channel sounding procedure” or simply “explicitsounding” is the process defined in 802.11 specifications where APtransmissions are channel estimated by the STA, and then fed back to theAP, providing it with the magnitude of phase and amplitude differencesbetween the signals as transmitted by the AP vis-à-vis as received bythe client/STA, allowing it to gauge or measure possible distortions andcorrect them.

Associated STA is defined herein as a STA that is served by a certain APwith a certain Service Set Identifier (SSID).

Non-associated STA is defined herein as a STA within the range of thenon-serving AP.

The acronym “NAV” stands for Network-Allocation-Vector and representsvirtual carrier sense mechanism, used by a Wi-Fi transmitting message tobroadcast the predicted duration of its transmission, signaling to othernodes for how long 1 the channel be occupied.

The acronym “RTS” stands for Request-To-Send, and represents a messagetransmitted by one Wi-Fi node to another, probing it for informationabout its availability to receive data, per the Wi-Fi Alliance protocol.

The acronym “CTS” stands for Clear-To-Send, and represents a positiveresponse from the other node to the node originating the RTS, indicatingto the requesting node that the channel is clear from its point of viewas well.

The notation “DURATION” is a message embedded in both RTS and CTS,representing a prediction of the future traffic about to be transmittedbetween two nodes that have captured the channel; other nodes thatreceive it, must clear the channel as long as the DURATION has notexpired; other nodes that have received the RTS but received the CTS(hidden nodes) will avoid accessing the channel, allowing the receivingnode to successfully complete the reception.

The acronym “FLA” stands for Fast Link Adaptation, and representsprocesses that reduce transmitting side learning time of the receiver'sSINR.

The acronym “MCS” stands for Modulation Coding Scheme, mapping SINR tomodulation order and code rate.

The acronym “MRQ” stands for MCS request (Modulation Code SchemeRequest)

The acronym “MSI” stands for MRQ Sequence Identifier, which carries MCSfeedback from receiver to transmitter.

The term “null” as used herein, is a spatial pattern, created by two ormore antennas, formed in such a way that significantly reduces the powerlevel received by a given receiver (e.g., a local minimum). An “Rx Null”is a null formed by a receiver's antennas weight in order to decreaseundesired signal level. A “Tx Null” is formed by transmitter's antennasweights in order to decrease its undesired transmitted signal at remotereceiver's input.

The term “actual null depth” as used herein, is the estimated value ofthe null after a certain time period has elapse since the last explicitsounding in which the amplitude and the phase have drifted so as toyield null degradation. The actual null depth is the original nulltaking account the estimated null degradation.

The term “AP Beacon” is a management signal that is transmitted atregular intervals (typically about 10 times per second) that indicatescapability of the AP. The Beacon frame contains both mandatoryinformation (such as SSID) and optional data that may include vendorspecific information.

NDP represents Null Data Packet, transmitted by a Beamformer Nodetowards a Beamformee Node.

Compressed beamforming represents a data packet transmitted by aBeamformee Node towards a Beamformer Node as a response to a NDP; itcomprised of a channel estimation matrix including all combinations of NBeamformee and M beamformer antennas.

Reciprocity calibration as defined herein is a process in which two TDDNodes exchange transmissions, perform receptions, and calculatebeamforming settings, so that the channel matrix values measured betweenthe antennas of a first node and a second node in one direction, can bemodified via said calibration process so that when used in the otherdirection, will be perceived by the other node with the same channelmatrix values.

According to current IEEE 802.11 air protocols, two APs may downloadtraffic over the same frequency channel to their respective STAs at thesame time as long as these APs are not within CCA range of each other.When an RTS/CTS procedure is used, an additional condition isintroduced, namely, a legacy STA receiving the download traffic from itsserving AP, must not be within CCA range of other transmittingneighboring AP or STA.

It should be noted that the notations I, J, K given in capital letters,are not related to the notations i, j, k given in lower case.

SUMMARY OF THE INVENTION

In many deployments APs sharing the same radio channel are within CCArange of each other. Thus, an AP may be blocked from transmitting to itsclient STA due to activity of a neighboring AP. An AP equipped withtransmitting and receiving MIMO, may enhance its signal to its clientSTA while simultaneously nulling its signal toward the interfering AP.Gaining knowledge of the AP-AP channel may be done using AP-AP explicitsounding procedure.

However, the aforementioned method may only accommodate low mobilityenvironments, where neighboring APs are updating each other's channelknowledge via explicit sounding in between packets or several packets,assuming drift accumulated over time elapsed from last measurement isminimal At high mobility environments the aforementioned methodestimates nulling capability deterioration based on measured fadinggradients, and accordingly conducts nulling capabilities qualificationbefore deciding on accessing the neighboring AP occupied channel.

Embodiments of the present invention disclose a MU-MIMO procedure, whichenables a neighboring AP to access a channel already occupied by anotherdownloading AP, is disclosed at AP-AP explicit sounding patent.

Embodiments of the present invention may require that the APsparticipating will be listed (e.g. “on the list”) of the AP Sounding Set(APSS), being a cluster of APs that work together with mutual soundingprocess to reduce interference.

Each AP performs APSS initialization by surveying the neighboringco-channel APs periodically, listing those who are within its CCA range,eliminating from the list legacy APs which do not adhere to the APSSprotocol. An AP member of the APSS group may then perform a periodicAPSS sounding versus all appearing on their list, or versus those thatcause most of the blocking it experiences.

Additionally, the AP also performs an implicit measurement each time anexplicit one is taking place, for example, it registers the complexvalues of uplink signals transmitted by each of the neighbor's antennas,as received by each of its receiving antennas, across the bandwidth; theimplicit measurement is then compared to the explicit one, and acalibration factors per subcarrier may be derived.

Once the AP is contemplating to download a packet to a STA client whilethe channel is already occupied by one of its listed neighboring APs, itperforms an updated implicit measurement of the neighbor, then retrievesthe last stored the calibration factor; the calibration factor is alsosubject to updates, in order to address mobility and fading that mayintroduce channel variations.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best bemore fully understood by reference to the following detailed descriptionwhen read with the accompanying drawings in which:

FIG. 1 is a block diagram illustrating two neighboring multi antennaaccess points deferring to each other when within CCA range according tothe prior art;

FIG. 2 is a block diagram illustrating two neighboring multi antennaaccess points, which may simultaneously use the same channel undercertain conditions in accordance with some embodiments of the presentinvention;

FIG. 3 is an example of an AP block diagram with firmware upgradesenabling both explicit and implicit AP to AP sounding in accordance withsome embodiments of the present invention;

FIGS. 4 and 5 are block diagrams, illustrating dual sounding procedure,in which an AP reuses a channel occupied by another AP within CCA rangein accordance with some embodiments of the present invention;

FIGS. 6 and 7 are block diagrams, illustrating various Receive andTransmit components in both Beamformer and Beamformee nodes thatcontribute to phase and amplitude deflections in accordance with someembodiments of the present invention;

FIG. 8 depicts a novel Explicit-Implicit sounding procedure inaccordance with some embodiments of the present invention;

FIG. 9 is a flowchart diagram illustrating polling of explicit andimplicit information by one AP from another, in accordance with someembodiments of the present invention;

FIG. 10 depicts calibration process of implicit measurement by anexplicit sounding data, in accordance with some embodiments of thepresent invention;

FIG. 11 is a flowchart diagram illustrating a method of usingExplicit-Implicit sounding procedure between 2 APs in order to share thechannel (under certain conditions) in accordance with some embodimentsof the present invention;

FIG. 12 depicts a method of addressing mobility and fading channelvariation, in accordance with some embodiments of the present invention;

FIG. 13 is a flowchart diagram illustrating method to use Beacontransmission to Broadcast an APSS capability in accordance with someembodiments of the present invention;

FIG. 14 is a diagram illustrating an 802.11 Preamble field example inaccordance with some embodiments of the present invention;

FIG. 15 is a diagram illustrating a Preamble antenna identificationtagging in accordance with some embodiments of the present invention;

FIG. 16 shows measurement of phase and amplitude differences between upand down link of time, as measured in an office environment, using802.11 AP and client, done while people are walking around, generatingfading environment., in accordance with some embodiments of the presentinvention;

FIG. 17 shows computer simulated graphs illustrating the impact offading on amplitude and phase differences between up and down link, andthe impact it has on null depth, in accordance with some embodiments ofthe present invention; and

FIG. 18 shows computer simulated graphs illustrating the impact offading on amplitude and phase differences between up and down link, andthe impact it has on null depth, when 1^(st) order corrections areimplemented, in accordance with some embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Prior to setting forth the detailed description of the invention, it maybe helpful to set forth definitions of certain terms and acronyms thatwill be used hereinafter in describing embodiments of the presentinvention.

“APSS” is an acronym for AP Sounding Set. This is a cluster of APs thatworks together with mutual AP-AP sounding process to reduce interferenceaccording to embodiments of the present invention. An AP may indicatethat it is APSS-capable (e.g. capable in participating in a mutualsounding process) via its AP beacon signal.

“APSS-AP” indicates an AP which is compatible with APSS, meaning it isequipped with special software so that it can participate in APSS,either as a sounder or as a responder.

“APSS-AP_1” is the AP that initiates the APSS process. If multipleAPSS-APs are present, then multiple APSS's exist.

“APSS_ID” is a K bit random code selected by APSS-AP_1 to identify theAPSS that it has created

“APSS-AP_i” is an AP member in a group of APs that is a recipient of anAPSS-AP_1's initiation of an APSS process, where I {2 . . . K} is thedesignator for the different APSS-AP that are members of the APSS_ID.Also labeled as “Compatible Access Point”.

“APSS-I-AP” is an AP being an improved version of APSS-AP and capable ofboth APSS explicit sounding of neighboring APSS-APs as explained above,as well as implicit channel estimation carried out while a respondingcompressed beamforming is received by the APSS-I-AP from and APSS-AP,and using it for calibration of implicit measurements that follow whennulling of neighboring APSS-APs is performed.

In the following description, various aspects of the present inventionwill be described. For purposes of explanation, specific configurationsand details are set forth in order to provide a thorough understandingof the present invention. However, it will also be apparent to oneskilled in the art that the present invention may be practiced withoutthe specific details presented herein. Furthermore, well-known featuresmay be omitted or simplified in order not to obscure the presentinvention.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing,” “computing,”“calculating,” “determining,” or the like, refer to the action and/orprocesses of a computer or computing system, or similar electroniccomputing device, that manipulates and/or transforms data represented asphysical, such as electronic, quantities within the computing system'sregisters and/or memories into other data similarly represented asphysical quantities within the computing system's memories, registers orother such information storage, transmission or display devices.

Embodiments of the present invention provide an improvement to aconfiguration of two 802.11 MU-MIMO capable neighboring access points,which perform from time to time explicit channel sounding of each other.Explicit AP-AP sounding may be carried out in a manner similar to themethodology of AP-to-STAs sounding process of 802.11ac, wherein APssound each other via Null-Data-Package (NDP) transmissions andcompressed beamforming responses. Explicit AP-AP sounding providesaccurate downlink channel knowledge each time it is applied, yet thefrequency of application is limited by the overhead it creates,therefore, effective nulling can be applied within few millisecondsafter the sounding, as time intervals grow, the channel changes and thenull depth is reduced.

Embodiments of the present invention provide a method of combining AP-APexplicit sounding with implicit sounding, thus maintaining high nullingcapability even when the last sounding took place considerable amount oftime earlier.

FIG. 1 illustrates access points AP_1 101 and AP_2 103 deployed withinthe CCA range 105 of AP_1, wherein both AP_1 and AP_2 use the same802.11 channel in accordance with the prior art. It is assumed that thechannel was occupied by yet another 802.11 node that made both AP_1 andAP_2 waiting for it to clear the channel, and that AP_2 has transmitteda Preamble slightly before AP_1 was about to transmit its Preamble, andconsequently the channel was captured by AP_2, which then startedserving its 104 client STA_2 with a download packet 111.

Being a co-channel Wi-Fi access point (e.g., IEEE 802.11ac), AP_1 isprohibited from accessing the channel and has to wait for the channel toclear again. It is further depicted in FIG. 1 that in a hypotheticalcase wherein AP_1 would have nevertheless violated the rule andproceeded to download a packet 106 to its 102 client STA_1, theimmediate results of the two APs transmitting download 108, 109 packetsto their respective client STAs in the illustrated apparatus, would notbe harmful to the transmitters 101, 103, but would potentially jam thereception of acknowledgements 107, 110.

FIG. 2 illustrates APs APSS-I-AP_1 201 and APSS-I-AP_2 203, according toembodiments of the present invention. The APSS-I-APs are similar to theAPs in FIG. 1, with the difference that: APSS-I-AP_1 201 and APSS-I-AP_2203 are provided with APSS capabilities APSS-I-APAPSS-I-AP. In essence,APSS-I-AP_1 is capable of forming such a transmit null towards one ormore antennas of APSS-I-AP_2, enabling it to access the channelpreviously occupied by APSS-I-AP_12 without harming the proper receptionof acknowledgement 210 coming from STA_2 204, under certain conditions.

While forming a transmitting null towards APSS-I-AP_2, APSS-I-AP_1 isalso capable of forming a receiving null towards one or more of theinterference components of APSS-I-AP_2 data streams 208, providing somelevel of protection for receiving acknowledgment 207 from its clientSTA2 under certain conditions.

FIG. 3 is a block diagram 300 illustrating an exemplary high levelarchitecture of an APSS-I-AP_1 300 according to some embodiments of theinvention. APSS-I-AP_1 300 has the structure of a typical IEEE 802.11acAP with a rank 2×2 MIMO receive/transmit configuration or higher. Afirst RF chain starts from an antenna 307 that feeds a plurality ofradio circuits 308 configured to transmit and receive signals via theplurality of antennas (e.g. 307). Radio circuits 308 may include aswitch 306, which in turn feed an LNA 305 and a down-converter 303, andbeing fed by a power amplifier 304 and an up-converter 302. A second RFchain, may start with antenna 325 and radio circuits 326 may include aswitch 324, which in turn feeds a LNA 323 and a down-converter 321, andis fed by (e.g. receives signals from) a power amplifier 322 and anup-converter 320. Similar RF chains can be provided (not shown) allstructured in a similar way with its own antennas and RF circuits.

All of the aforementioned RF chains are connected to the APSS-I-APbaseband processor 301, which may comprised of a legacy 802.11ac orhigher release, capable of receiving and transmitting a 2×2 MIMO rank orhigher, and is further capable of performing Multi-User MIMO (MU-MIMO)operation.

Additionally, in accordance with embodiments of the present invention,baseband processor 301 may be provided with DSP and firmware upgradesenabling APSS and Implicit AP-AP sounding. These upgrades provides thefunctionalities that makes access point 300 both APSS compatible andfurther capable in participating in mutual AP-AP implicit soundingprocedure. For example, these upgrades enable baseband processor 301 tomonitor signals received by radio circuits 308 and generate a list ofneighboring co-channel access points, that each has plurality ofantennas and are further located within a clear channel assessment (CCA)range of the access point.

FIG. 4 is a block diagram 400 illustrating potential deployment of theaccess points according to embodiments of the invention. Access point401 is operating within the CCA ranges of several neighboring APSScapable access points 402, 403, and 404. In operation, AP 401 may beconfigured to broadcast, at time T_(i) an NDP announcement to bereceived at all APSS-capable access points 402, 403, and 404. Thebroadcast in accordance with embodiment of the present invention differsfrom an NDP announcement broadcast according to the MU-MIMO IEEE802.11ac standard in which the NDP announcement is broadcasted by an APand may be directed at STAs that would be then the served STAs at theMU-MIMO transmission scheme. Specifically, the NDP announcementbroadcast according to embodiments of the present invention is conductedby an AP and is directed at neighboring APs that are further providedwith the APSS capability. The neighboring APs will not be served by thebroadcasting AP but rather, the sounding procedure will provide dataindicative of how to access an already occupied channel withoutinterfering with neighboring APs serving their STAs.

FIG. 5 illustrates a system 500 according to embodiments of theinvention, wherein access point APSS-I-AP_1 501 may be an AP capable ofperforming explicit sounding of neighboring APs as well as implicitsounding of the neighboring APs, operating within the CCA range ofseveral neighboring APSS-capable APs, APSS-I-AP_2 502, APSS-I-AP_3 503,and APSS-I-AP_4 504. Each of neighboring APSS capable APs may beassigned with its own time slot similarly to time slots set for stationsin the IEEE 802.11ac standard (e.g. T_(i+1), T_(i+2) and T_(i+3) inwhich they are configured to unicast to AP 501 the compressed channelmatrix holding the channel data. As in FIG. 4, the system depicteddiffer from IEEE 802.11ac standard in that the nodes participating inthe sounding are AP both as the beamformer and beamformees. The soundingset generated following the broadcast depicted in FIG. 5 and the unicasttransmission depicted in FIG. 5 is for access points only.

FIGS. 6 and 7 are block diagrams showing all components of in anend-to-end scheme (e.g. baseband to baseband) of two access pointshaving a communication link between them. Specifically FIG. 6 focuses ontransmission from access point A to access point B while FIG. 7 focuseson transmission from access point B to access point A. FIGS. 6 and 7illustrate the various signal degradations, apart from the channel, thatneed to be taken into account in calibrating the implicit soundingmeasurements since the end-to-end channel from access point A to accesspoint B and the end-to-end channel from access point B to access point Aare not reciprocal.

More specifically, FIG. 6 depicts a system 600 including access points Aand B. Access point A with baseband processor 601, up and downconverters 602, 603, respectively, Power Amplifier and Low NoiseAmplifier 604, 605, respectively, an RF switch 606 that select eithertransmission or reception through the common antenna 607. Access Point Bincludes baseband processor 608, up and down converters 609, 610,respectively, Power Amplifier and Low Noise Amplifier 611, 612,respectively, an RF switch 613 that selects transmission or receptionthru the common antenna 614.

Access Point A SigIn₁ signal 615 from baseband processor 601, which ispassed through the RF chain 602, 604, 606, 607, propagates through thechannel 617, received by the RF chain 614, 613, 612, 610 of Access PointB and fed to baseband processor 608 as SigOut₁ 616.

FIG. 7 depicts system 700 including access points A and B. Access pointA with baseband processor 701, up and down converters 702, 703,respectively, power amplifier and Low Noise Amplifier 704, 705,respectively, an RF switch 706 that select either transmission orreception thru the common antenna 707. Access point B includes basebandprocessor 708, up and down converters 709, 710, respectively, poweramplifier and Low Noise Amplifier 711, 712, respectively, an RF switch713 that select either transmission or reception through the commonantenna 714. Access point B SigIn₂ signal 716 from baseband 708, whichis passed through the RF chain 709, 711, 713, 714, propagates thru thechannel 717, received by the RF chain 707, 706, 705, 703 of Access PointA and fed to baseband processor 701 as SigOut₂ 715.

According to embodiments of the invention, Access point A may beconfigured to compare the Null-Data-Package transmitted as SigIn₁ withthe response received as SigOut₂, so that access point A can thusestimate and eliminate Rx/Tx circuitry distortions in both sides (e.g.from A to B and from B to A).

In order to mathematically formulate a solution for estimating the Rx/Txcircuitry distortions on both sides, we may start in calculating theSigOut₁ 616 as a function of SigIn₁ 615 at time T. As derived from FIG.6, SigOut_(i) 616 may be given in Eq. 1 below as being affected byvarious factors (FACT) as follows:Sig_(out1)(freq_(k),Chan_(J))=FACT_(upconv)(A,freq_(k),Chan_(I))·FACT_(PA)(A,freq_(k),Chan_(I))·FACT_(SWT)(A,freq_(k),Chan_(I))·FACT_(Ant)(A,freq_(k),Chan_(I))·FACT_(propag)(T,I,J,freq_(k))·FACT_(Ant)(B,freq_(k),Chan_(J))·FACT_(SWR)(B,freq_(k),Chan_(J))·FACT_(LNA)(B,freq_(k),Chan_(J))·FACT_(dwnconv)(B,freq_(k),Chan_(J))·Sig_(in1)(freq_(k),Chan_(I))  Eq.1

Where:

FACT_(upconv)(A,freq_(k),Chan_(I)) denotes the signal distortion of theup convertor in channel “I” in AP “A” at freq “k”;

FACT_(dwnconv)(B,freq_(k),Chan_(J)) denotes the signal distortion ofdown convertor in channel “J” in AP “B” at freq “k”;

FACT_(PA)(A,freq_(k),Chan_(I)) denotes the signal distortion of PA inchannel “I” in AP “A” at freq “k”;

FACT_(LNA)(B,freq_(k),Chan_(J)) denotes the signal distortion of LNA inchannel “J” in AP “B” at freq “k”;

FACT_(SWT)(A,freq_(k),Chan_(I)) denotes the signal distortion of SW inTX path in channel “I” in AP “A” at freq “k”;

FACT_(SWR)(B,freq_(k),Chan_(J)) denotes the signal distortion of SW inRX path in channel “J” in AP “B” at freq “k”;

FACT_(Ant)(A,freq_(k),Chan_(I)) denotes the signal distortion of antenna“I” in AP “A” at freq “k”;

FACT_(Ant)(B,freq_(k),Chan_(J)) denotes the signal distortion of antenna“J” in AP “B” at freq “k”;

FACT_(propag) (T,I,J,freq_(k)) denotes the distortion due to propagationbetween channel “I” and channel “J” in freq “k” at time T;

Similarly, as may be derived from FIG. 7, SigOut₂ 715 as a function ofSigIn₂ 716 at time T may be given in Eq. 2 below:Sig_(out2)(freq_(k),Chan_(I))=FACT_(upconv)(B,freq_(k),Chan_(J))·FACT_(PA)(B,freq_(k),Chan_(J))·FACT_(SWT)(B,freq_(k),Chan_(J))·FACT_(Ant)(B,freq_(k),Chan_(J))·FACT_(propag)(T,I,J,freq_(k))·FACT_(Ant)(A,freq_(k),Chan_(I))·FACT_(SWR)(A,freq_(k),Chan_(I))·FACT_(LNA)(A,freq_(k),Chan_(I))·FACT_(dwnconv)(A,freq_(k),Chan_(I))·Sig_(in2)(freq_(k),Chan_(I))  Eq.2

Where:

FACT_(upconv)(B,freq_(k),Chan_(J)) is the signal distortion of upconvertor in channel “J” in AP “B” at freq “k”;

FACT_(dwnconv)(A,freq_(k),Chan_(I)) is the signal distortion of downconvertor in channel “I” in AP “A” at freq “k”;

FACT_(PA)(B,freq_(k),Chan_(J)) is the signal distortion of PA in channel“J” in AP “B” at freq “k”;

FACT_(LNA) (A,freq_(k),Chan_(I)) is the signal distortion of LNA inchannel “I” in AP “A” at freq “k”;

FACT_(SWT)(B,freq_(k),Chan_(J)) is the signal distortion of SW in TXpath in channel “J” in AP “B” at freq “k”;

FACT_(SWR)(A,freq_(k),Chan_(I)) is the signal distortion of SW in RXpath in channel “I” in AP “A” at freq “k”;

FACT_(Ant)(B,freq_(k),Chan_(J)) is the signal distortion of antenna “J”in AP “B” at freq “k”;

FACT_(Ant)(A,freq_(k),Chan_(I)) is the signal distortion of antenna “I”in AP “A” at freq “k”; and

FACT_(propag)(T, I,J,freq_(k)) denotes the distortion due to propagationbetween channel “I” and channel “J” in freq “k” at time T same as in theother direction (for the same time)

As explained above, in addition to explicit sounding, the APSS-I-AP mayalso performs an implicit measurement each time an explicit one istaking place, e.g., the APSS-I-AP registers the complex values of uplinksignals transmitted by each of the neighbor's antennas, as received byeach of its receiving antennas, across the bandwidth. The implicitmeasurement is then compared to the explicit one, and a calibrationfactors per subcarrier may be derived.

Once the APSS-I-AP is contemplating to download a packet to a STA clientwhile the channel is already occupied by one of its neighboringAPSS-I-AP (which is on its APSS list), it performs an updated implicitmeasurement of the neighbor (without an explicit sounding), thenretrieves the last stored calibration factor, followed by a correctionbased on 1^(st) order, or 2^(nd) order or 3^(rd) order extrapolation,depending on the fading environment.

In FIG. 6, whenever AP “A” sends “B” an explicit calibration signal“NDP” this signal is a priori well known to both side, so that AP “B”can calculate the total end-to-end distortion as follows:

${{Distotion}\mspace{14mu}\left( {T_{1},A_{I},B_{J},{freq}_{k}} \right)} = \frac{{Sig}_{{out}\; 1}\left( {{freq}_{k},{Chan}_{J}} \right)}{{Sig}_{{in}1}\left( {{freq}_{k},{Chan}_{J}} \right)}$Distotion(T ₁ ,A _(I) ,B_(J),freq_(k))=FACT_(upconv)(A,freq_(k),Chan_(I))·FACT_(PA)(A,freq_(k),Chan_(I))·FACT_(SWT)(A,freq_(k),Chan_(I))·FACT_(Ant)(A,freq_(k),Chan_(I))·FACT_(propag)(T₁,I,J,freq_(k))·FACT_(Ant)(B,freq_(k),Chan_(J))·FACT_(SWR)(B,freq_(k),Chan_(J))·FACT_(LNA)(B,freq_(k),Chan_(J))·FACT_(dwnconv)(B,freq_(k),Chan_(J))  Eq.3

Where T₁ is the measurement taken at time T₁.

This comprehensive end-to-end data is sent back as a reply to AP “A” inreduced (e.g. compressed) form so that AP “A” can expand the NDP messageand know the end-to-end distortion that is accurate for the time themeasurement is made (time of the calibration message) after some timedue to change in propagation condition the distortion value isinaccurate, therefore the distortion value is valid only after a shortinterval after the calibration message is sent.

In order to maintain good nulling condition frequent explicitcalibration message may be applied. However, frequent explicit soundingis not practical since neighboring APs may be polled only when they areneither transmitting nor receiving data to or from their own clientSTAs, and so explicit sounding of them may be done only sporadically, atidle moments.

In implicit sounding, AP “A” receives an opportunistic transmission from“B” not necessarily intended to it, all transmissions include a traininginterval where the transmit signal and antenna is well known to all side(protocol dependent), from this training interval AP “A” may derive theoverall channel distortion from “B” to “A” as formulated below:

${{Distotion}\mspace{14mu}\left( {T_{2},B_{J},A_{I},{freq}_{k}} \right)} = \frac{{Sig}_{{out}\; 2}\left( {{freq}_{k},{Chan}_{I}} \right)}{{Sig}_{{in}2}\left( {{freq}_{k},{Chan}_{I}} \right)}$Distotion(T ₂ ,B _(J) ,A_(I),freq_(k))=FACT_(upconv)(B,freq_(k),Chan_(J))·FACT_(PA)(B,freq_(k),Chan_(J))·FACT_(SWT)(B,freq_(k),Chan_(J))·FACT_(Ant)(B,freq_(k),Chan_(J))·FACT_(propag)(T₂,I,J,freq_(k))·FACT_(Ant)(A,freq_(k),Chan_(I))·FACT_(SWR)(A,freq_(k),Chan_(I))·FACT_(LNA)(A,freq_(k),Chan_(I))·FACT_(dwnconv)(A,freq_(k),Chan_(I))  Eq.4

Where T₂ is the measurement time T₂.

This information is also generated from the reply message of B to Aduring the explicit calibration at time T, e.g. Distotion(T₁, B_(J),A_(I), freq_(k)). Then by dividing eq 3 by 4 for time T₁ may be derivedusing equation 1 and 2:

$\begin{matrix}{{{Ratio}\mspace{14mu}\left( {T_{1},A_{I},B_{J},{freq}_{k}} \right)} = \frac{{Distotion}\mspace{14mu}\left( {{T_{1,}A_{I}},B_{J},{freq}_{k}} \right)}{{Distotion}\mspace{14mu}\left( {{T_{1,}B_{J}},A_{I},{freq}_{k}} \right)}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$Ratio(T ₁ ,A _(I) ,B_(J),freq_(k))={FACT_(upconv)(B,freq_(k),Chan_(J))·FACT_(PA)(B,freq_(k),Chan_(J))·FACT_(SWT)(B,freq_(k),Chan_(J))·FACT_(SWR)(A,freq_(k),Chan_(I))·FACT_(LNA)(A,freq_(k),Chan_(I))·FACT_(dwnconv)(A,freq_(k),Chan_(I))}/{FACT_(upconv)(B,freq_(k),Chan_(J))·FACT_(PA)(B,freq_(k),Chan_(J))·FACT_(SWT)(B,freq_(k),Chan_(J))·FACT_(SWR)(A,freq_(k),Chan_(I))·FACT_(LNA)(A,freq_(k),Chan_(I))·FACT_(dwnconv)(A,freq_(k),Chan_(I))}  Eq.6

As can be seen from Eq. 6, the fast moving factorFACT_(propag)(I,J,freq_(k)) may be reduced as well as the antennasfactor, so that this ratio is quasi-static, e.g. slowly independent oftime.

Embodiments of the present invention provide a manner by whichtransmissions from AP “B’ that can be used by AP “A” to generate the Bto A distortion at time T₂, T₃ etc. For example at time T_(n):

${{Distotion}\mspace{14mu}\left( {T_{n},B_{J},A_{I},{freq}_{k}} \right)} = \frac{{Sig}_{{out}\; 2}\left( {{freq}_{k},{Chan}_{I}} \right)}{{Sig}_{{in}2}\left( {{freq}_{k},{Chan}_{I}} \right)}$

Following the above calculation, the opposite overall distortion due toelectronic circuits from A to B may also be estimated and thuseliminated, thereby allowing the use of implicit sounding sue to thecalibration process depicted above.

FIG. 8 is a block diagram 800 illustrating a system and a flow combiningexplicit and implicit soundings in accordance with embodiments of thepresent invention. A beamformer access point APSS-I-AP 805 may broadcastan NDP announcement followed by an NDP to listed neighboring accesspoints APSS-I-AP, including beamformer access point 801. The NDP may betransmitted from M antennas 804, over the channel 803, received throughN antennas 802, and fed into access point APSS-I-AP 805 and itsbaseband.

As a results, the baseband processor of access point APSS-I-AP 801,which is configured to respond to such sounding, sends back a compressedbeamformer message 806, and appends to that message a set of N pilots807, each transmitted from a different one of the N antennas.

In some embodiments of the invention, the compressed beamforming messagemay be arranged in a N×M block, having N subgroups, each for one of thebeamformee antennas, and the subgroups may each have M data entities,one for each of the M beamformer antennas. In some embodiments of theinvention, the N pilots may be constructed of N pairs of symbols, eachpair transmitted from a different beamformee antenna of the N antennas.

FIG. 9 is a flowchart 900 illustrating an exemplary sequence of explicitand implicit information retrieval in accordance with embodiments of theinvention. Illustrated in the flowchart is an explicit sounding betweenAPSS-I-APs, carried out from time to time or periodically, withaugmentation of implicit sounding. The sounding process of a beamformerAPSS-I-AP may be conducted vis-à-vis a chosen set of neighboringAPSS-I-APs, which may be APs within CCA range of the first APSS-I-APconfigured to operate according to the present invention. The processstarts at step 901 when beamformer APSS-I-AP transmits downlink NullData Packet (NDP) Announcement. Then, in step 902, beamformer APSS-I-APtransmits Null Data Packet to beamformee APSS-I-AP_i. In step 903,beamformee APSS-I-AP_i performs channel estimation via its N antennas,for each of beamformer's M antennas. In step 904, beamformee APSS-I-AP_iprepares a compressed beamforming message, arranged in N×M block format,ordered in N subgroups, each containing M channel estimation data,corresponding to N beamformee and M beamformer antennas. In step 905,beamformee APSS-I-AP_i transmits the compressed response and appends Npairs of pilot symbols, each transmitted via one of its N antennas atthe same arranged N subgroups order. Then, in step 906, the beamformerAPSS-I-AP stores the N×M compressed beamformer message in a first memoryspace, and the received N pilots channel estimations in a second memoryspace. A mapping between explicit and implicit signatures enables thegeneration of calibration lookup table, that allows corrections ofimplicit measurements carried out just before nulling, as describedherein. The Implicit-Explicit mapping may be carried out in step 906 byusing beamformer APSS-I-AP baseband to store explicit data in a firstmemory space, and Implicit data in a second memory space, at apredefined arranged order.

FIG. 10 is a flowchart 1000 illustrating the method in accordance withembodiments of the present invention of using explicit data to calibrateimplicit channel estimation measurements. In step 1001, APSS-I-APperforms from time to time APSS explicit sounding of one or moreneighboring APSS-I-APs. According to embodiments of the invention, inthe sounding routine, APSS-I-AP may perform explicit sounding versuslisted neighboring APSS-I-APs. In step 1002, neighboring APSS-I-APsrespond with a combination of explicit compressed beamforming andtransmission of N pilots. In step 1003, the baseband processor ofbeamformer APSS-I-AP stores explicit data in a first memory space usingN×M entries X_(ij), labeled as reference weights. Indices i, j, rangefrom 1 to N and from 1 to M, respectively, which are received by thebeamformer APSS-I-AP and stored in a first memory space and furtherreferred to as reference data. In step 1004, beamformer APSS-I-APbaseband stores implicit channel estimation of the N pilots in a secondmemory space entries Y, labeled as implicit weights, where i, j, rangefrom 1 to N and from 1 to M, respectively and are stored in a secondmemory space. In step 1005, the baseband processor of beamformerAPSS-I-AP calculates correction ratio factors Z=X_(ij)/Y_(ij) that areused to modify recent implicit channel estimations according topreviously measured explicit references. In step 1006, the basebandprocessor of beamformer APSS-I-AP stores Z_(ij) correction factors in acalibration lookup table. In step 1007, in the event beamformerAPSS-I-AP is contemplating accessing a channel has recently beenoccupied by a neighboring APSS-I-AP via applying a null, it uses thelast stored implicit channel estimation of the neighboring preamble,multiplies it by the look up table calibration factors Z_(ij) andapplies the resultant weights for null calculation.

In other words, whenever an APSS-I-AP attempting to access a previouslyoccupied channel by a neighboring APSS-I-AP via nulling, an implicitchannel estimation of the neighboring APSS-I-AP is performed to yield ameasurement, and the last registered calibration factors Z_(ij) is usedto correct the measurement.

FIG. 11 is a flowchart 1100 illustrating the way the explicit-implicitcalibration may be used by a APSS-I-AP_1 for accessing of a channel justcaptured by one neighboring APSS-I-AP_i. In step 1101 APSS-I-AP_1 has adownload packet scheduled, and attempts to access when the channel iscleared. In other words, APSS-I-AP_1 intends to download a packetscheduled to a client STA, or multiple clients STAs (in case ofAPSS-I-AP_1 MU-MIMO transmission). In step 1102 APSS-I-AP_i's preambleis detected, and APSS-I-AP_1 performs and registers channel estimationof the preamble. More specifically, the interception of a preamble andan indication of preamble antenna from a neighboring APSS-I-AP_i, andthe performance of the preamble channel estimation by APSS-I-AP_1 areillustrated. In step 1103 APSS-I-AP_1 verifies that conditions for APSSare fulfilled. The set of topologic conditions and qualifications thatare verified before an APSS_AP_1 may perform an APSS process and accessthe busy channel: The beamformer AP is outside the CCA range of the STAcurrently served by the beamformee AP; The beamformee AP is outside theCCA range of the STA to be served by the beamformer AP; Both served STAsare verified to be located closer than the edge of their serving cells,since their corresponding APSS-AP's′ sensitivity is slightly reduced byminor residual interference caused by the APSS process. In order toguarantee the APSS-AP_i session is not harmed by the APSS_AP_1 access, anull depth verification and validation is required.

In step 1104 APSS-I-AP_1 uses calibration table between implicit andexplicit measurements for correction of the implicit measurement, anduses the results to calculate accurate channel estimation of theAPSS-I-AP_i antenna that has emitted the preamble

In step 1105 APSS-I-AP_1 calculates weights for its transmittingantennas, which will serve a client STA or STAs, while projecting a nulltowards the transmitted Preamble's APSS-I-AP-i antenna, and in step 1106APSS-I-AP_1 accesses the occupied channel with a downlink packet towardsits client STAs, while projecting the null towards the APSS-I-AP_ipreamble antenna. Thus, the corrected Preamble channel estimation isused by APSS-I-AP_1, to create a transmit null towards the APSS-I-AP_i,while simultaneously serving its client STA or STAs with downlinkpackets.

It is noted that while explicit sounding provides highly accuratechannel estimation right after it is performed (e.g., fewmilli-seconds), it can be done only on a sparse or an infrequent basisas by nature it slightly penalizing the bandwidth of the participatingAPs, thus null quality is gradually compromised as time goes by, untilthe next explicit sounding takes place.

On the other hand, implicit sounding is done in great time proximity tothe application of a null (e.g., few milli-seconds), however, itsaccuracy is assumed lower than explicit sounding, since it relies ofself-calibrated up/down channel reciprocity.

Therefore, combining explicit and implicit, facilitates getting the bestof both worlds, granting close to immediate channel estimation implicitmeasurements the high accuracy achieved by sparse explicit channelestimation, thus reducing bandwidth exploitation penalty to a minimum.

In accordance of embodiments of the present invention the aforementionedmethod may include for example: transmitting and receiving signals via aplurality of M antennas and a plurality of radio circuits; monitoringthe signals received by the radio circuits and generating a list ofneighboring co-channel access points, that each has plurality of Nantennas and are further located within a clear channel assessment (CCA)range of the access point; instructing the radio circuits to transmit abeamformer sounding to the neighboring access points which are on thelist, according to a multi-user MIMO air-protocol, and receive from thebeamformee access points Channel State Information (CSI) that providesexplicit channel estimations information, and carrying out implicitchannel estimations procedure via beamformee's additional pilottransmissions appended to the explicit compressed beamforming data.

According to some embodiments of the present invention, the sounding maybe based on IEEE802.11ac air-protocol, wherein beamformee nodes of theIEEE802.11ac air-protocol or of later releases, are the neighboringaccess points instead of STAs, wherein compressed beamforming messageaccording to the IEEE802.11ac air-protocol or of a later release whichthe beamformee access points transmit back to the beamformer accesspoint, is arranged in a N×M blocks format, in or at an order that isknown to the receiving beamformer, and wherein the beamformee accesspoints are configured to transmit N pilots, following a transmission ofthe compressed-beamforming in an order that enables the beamformer tomap explicit data to implicit measurements.

According to some embodiments of the present invention, the explicitcompressed beamforming message sent by the beamformee, is ordered in Nsubgroups, each containing M channel estimation data corresponding to Nbeamformee and M beamformer antennas, and the implicit channelestimation is acquired by the beamformer access point via the beamformeeN pilots, each transmitted through a different one of its N antennas, ata same known order in which the compressed beamforming N×M blocks weretransmitted, so that the beamformer access point may map a given N_(i)received pilot to a N_(i) reported subgroup of the CompressedBeamforming message. According to some embodiments of the presentinvention, the beamformer access point is further configured to storethe compressed beamforming data in a first N×M memory space residing inthe baseband processor and labeled as reference measurements, andfurther configured to receive the N pilots with each of the M antennas,and store them in a second N×M memory space residing in the basebandprocessor, and referenced as implicit measurements, and wherein eachentry X_(ij) of the first N×M memory space is mapped to each entry Y₁ ofthe second N×M memory space, based on the known order of transmission.

According to some embodiments of the present invention, the procedure ofexplicit and implicit sounding processes are performed from time to timeand implicit-only sounding is performed before applying a null from oneaccess point to another.

According to some embodiments of the present invention, each entry Y₁ iscompared to the corresponding entry X_(ij) and a calibration factorZ_(ij) is calculated so that Z_(ij)=Y₁/X_(ij).

According to some embodiments of the present invention, a set of:X_(ij), Y_(ij), and Z_(ij) is stored as a calibration lookup table andwherein implicit sounding measurements Y₁ which are carried out withoutexplicit sounding, are corrected by Z_(ij) factor, before applyingnulling weighs calculations.

According to some embodiments of the present invention, the access pointmay be further configured to access a channel recently being occupied bya downloading listed neighboring access point, via performing channelestimation of the neighboring access point transmission, and applying areceive and a transmit null towards the neighboring access point,wherein the null weights are calculated using the implicit channelestimation, corrected by last stored calibration values Z_(ij).

The According to some embodiments of the present invention, the nullingcalculated for the neighboring access point that has recently occupiedthe channel is performed on the neighboring access point antenna whichhas just transmitted the Preamble received by the access point.

According to some embodiments of the present invention, the baseband maybe configured to keep records of previous explicit and implicit soundingprocesses done per each neighboring access point, and to calculateaverage differences between consecutive explicit reports, as well asaverage differences between their corresponding implicit channelestimations.

According to some embodiments of the present invention, the variations'averages, as well as a predicted gradient signs, are considered, as wellas the time elapsing between two consecutive explicit sounding takingplace amongst the access point and each of it listed neighboring accesspoints, in order to calculate a 1^(st) order correction.

According to some embodiments of the present invention, before using thecalibration lookup table reference values Z the access point uses theparameters to calculate a 1^(st) order correction factor U_(ij), to theZ_(ij) values, so that Z_(ij) ^((′))=Z_(ij)*U_(ij) is used to correctthe implicit channel estimation.

According to some embodiments of the present invention, the history ofExplicit Sounding is used to gauge or measure channel variation rate,via calculation of average or standard deviation or higher moments ofthe channel estimation data, and setting thresholds that categorize themobility level of the access point due to STAs, or objects and people intheir area of coverage.

FIG. 12 is a flowchart 1200 illustrating a process that estimateschannel variation over time and applies required correction to thereferences used for implicit channel estimation calibration; it is doneby a novel method where history of Explicit Sounding is used to gauge ormeasure channel variation rate via observation of the previous sounding,and the calculation of average or standard deviation or higher momentsof the channel estimation data, and setting thresholds that categorizethe mobility level of the access point due to STAs, or objects andpeople in their area of coverage. In step 1201 APSS-I-AP logs ExplicitSounding data reported from a given neighboring APSS-I-AP over time andestimates average variations ΔQ ij, and average period between explicitsounding events Δt. This step depicts one embodiment of quantifyingexplicit sounding history of cannel variation, done by estimatingchanges in the X_(ij) consecutive measurements and denoting them as ΔQij=X_(ij) (t_(q)−t_(q−1)) In step 1202 the average variations amount tonull depth flattening is checked to be greater than 3 dB.

In other words it depicts a metric where the total impact of all ΔQ ijmay cause inaccurate setting of a desired null that would reduce itsdepth by 3 dB or more. If such a null depth flattening is calculated, instep 1203 the average gradient between consecutive explicit soundings ofa given neighboring APSS-I-AP is estimated and in step 1204 the averagegradient between consecutive implicit soundings that were done inconjunction with the consecutive explicit soundings is estimated.Specifically, gradients calculation of both explicit and implicitprevious readings, may be used to correct the Z_(ij) references. In step1205 gradient sign predicted for the period following last explicitsounding is calculated based on the explicit and implicit averagegradients. Additionally, the history may be also used to predict thesign of the gradient. In step 1206, when APSS-I-AP contemplatesaccessing a channel occupied by a neighboring APSS-I-AP, the APSS-I-APbaseband may be configured to carry out an extrapolated correction tothe 1^(st) memory Z_(ij) calibration values, using average gradientvalue, predicted gradient sign, and the time elapsed since last explicitsounding of the neighbor. In step 1207 fading U_(ij)=f (ΔQ ij*t/Δt) isbeing calculated and reference values Z_(ij) ^((′))=Z_(ij)*U_(ij) may becorrected. The formula used for a correction factor to the references isgiven by U_(ij)=f(ΔQ ij*t/Δt), where Δt is the average time elapsedbetween consecutive explicit sounding. Then in step 1208, the accesspoint continues to access the channel. This is also the case when theaverage variations amount to null depth flattening is not greater than 3dB as check in step 1202.

FIG. 13 is a format diagram 1300 illustrating a novel tagging ofAPSS-I-APs' beacon transmission using the beacon frame 1301 asexplicit-implicit sounding-capable, thus allowing APSS-I-APs to identifycooperative AP neighbors. In one embodiment, this is done by using theOptional Management Elements field 1302 to transmit an APSS flag 1303 asshown in diagram 1300. In should be noted that other identificationmethods may be used to indicate an AP as explicit-implicitsounding-capable.

FIG. 14 illustrates the format structure 1400 of a legacy preamble inaccordance with the prior art and specifically the IEEE802.11acstandard. The left side illustrates the various fields for orthogonalfrequency-division multiplexing (OFDM) at binary phase shift key (BPSK)modulation using 1 of n antennas, whereas the right side illustrates thefield for very high throughput (VHT) modulation. The fields may include:legacy short training field (L-STF); legacy long training field (L-LTF);legacy signal (L-SIG); very high throughput signal-A (VHT SIG-A); andVHT short and long training, SU/MU MIMO training, plus data.

FIG. 15 is a diagram illustrating a novel tagging of the preamble'sunused bits for both SU-MIMO protocol format 1500A and for MU-MIMOprotocol format 1500B. Format diagram 1500A illustrates the Very HighThroughput—Signal—A (VHT-SIG-A) field for a single user format portionof 802.11 AC Preamble frame. VHT-Sig A-1 first orthogonalfrequency-division multiplexing (OFDM) symbol holds 24 bits. 22 bits areallocated by the standard. Two bits (Bit 0d02 and Bit 0d23) may bereserved for tagging the preamble in accordance with embodiments of thepresent invention. Also illustrated in format diagram 1500A is theVHT-Sig A-2 2^(nd) OFDM symbol which holds 24 bits, wherein 23 bits areassigned by the standard so that one bit (e.g., bit 0d09) may bereserved for tagging the preamble in accordance with embodiments of thepresent invention.

Similarly, format diagram 1500B illustrates VHT-SIG—A field for a multiuser format portion of 802.11 AC preamble frame. VHT-Sig A 1^(st) OFDMsymbol holds 24 bits: 22 bits are allocated by the standard and so twobits (bit 0d02 and bit 0d23) may be reserved for tagging the preamble inaccordance with embodiments of the present invention. Also illustratedin format diagram 1500B is the VHT-Sig A-2 2^(nd) OFDM symbol whichholds 24 bits, wherein 21 bits are assigned by the standard so that onebit (e.g., bits 0d07 through bit 0d09) may be reserved for tagging thepreamble in accordance with embodiments of the present invention.

In one embodiment two unused bits are required to designate each of theAP's 4 antennas, in another embodiment three bits are used for eightantennas' designation.

Unused bits in (a) SU-MIMO Preamble are 02, 23 of 1^(st) OFDM symbol and09 of 2^(nd) OFDM symbol; unused bits in (b) MU-MIMO are 02, 23 of1^(st) OFDM symbol and 07 through 09 of 2^(nd) OFDM symbol.

FIG. 16 illustrates an experimental results carried out with an 802.11AP deployed at an office environment, where up and down link phase andamplitude swing over time were recorded over time.

FIG. 17 illustrates a zero order correction applied to the test resultsof phase and amplitude drifts as a function of time for RMS, 90% and 95%of the cases, and the impact on the Power imbalance in dB (1701), thephase drift away from 180 degrees (1702) and the nulling capability(1703), starting at −40 dB close to the sounding event at 0 milli-sec(for 90% curve), and deteriorating to −14 dB at 10 milli-sec.

FIG. 18 illustrates a first order correction applied to the test resultsof phase and amplitude drifts as a function of time for RMS, 90% and 95%of the cases, and the impact on the Power imbalance in dB (1801), thephase drift away from 180 degrees (1802) and the nulling capability(1803), starting at −40 dB close to the sounding event at 0 milli-sec(for 90% curve), and deteriorating to some −27 dB at 10 milli-sec,demonstrating better performance than zero order.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or an apparatus.Accordingly, aspects of the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” For example, abaseband processor or other processor may be configured to carry outmethods of the present invention by for example executing code orsoftware.

The aforementioned flowcharts and block diagrams illustrate thearchitecture, functionality, and operation of possible implementationsof systems and methods according to various embodiments of the presentinvention. In this regard, each block in the flowchart or block diagramsmay represent a module, segment, or portion of code, which comprises oneor more executable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In the above description, an embodiment is an example or implementationof the inventions. The various appearances of “one embodiment,” “anembodiment” or “some embodiments” do not necessarily all refer to thesame embodiments.

Although various features of the invention may be described in thecontext of a single embodiment, the features may also be providedseparately or in any suitable combination. Conversely, although theinvention may be described herein in the context of separate embodimentsfor clarity, the invention may also be implemented in a singleembodiment.

Reference in the specification to “some embodiments”, “an embodiment”,“one embodiment” or “other embodiments” means that a particular feature,structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments, of the inventions. It will further berecognized that the aspects of the invention described hereinabove maybe combined or otherwise coexist in embodiments of the invention.

The principles and uses of the teachings of the present invention may bebetter understood with reference to the accompanying description,figures and examples.

It is to be understood that the details set forth herein do not construea limitation to an application of the invention.

Furthermore, it is to be understood that the invention can be carriedout or practiced in various ways and that the invention can beimplemented in embodiments other than the ones outlined in thedescription above.

It is to be understood that the terms “including”, “comprising”,“consisting” and grammatical variants thereof do not preclude theaddition of one or more components, features, steps, or integers orgroups thereof and that the terms are to be construed as specifyingcomponents, features, steps or integers.

If the specification or claims refer to “an additional” element, thatdoes not preclude there being more than one of the additional element.It is to be understood that where the specification states that acomponent, feature, structure, or characteristic “may”, “might”, “can”or “could” be included, that particular component, feature, structure,or characteristic is not required to be included.

Where applicable, although state diagrams, flow diagrams or both may beused to describe embodiments, the invention is not limited to thosediagrams or to the corresponding descriptions. For example, flow neednot move through each illustrated box or state, or in exactly the sameorder as illustrated and described. The descriptions, examples, methodsand materials presented in the claims and the specification are not tobe construed as limiting but rather as illustrative only.

Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined.

The present invention may be implemented in the testing or practice withmethods and materials equivalent or similar to those described herein.While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as exemplifications of some of thepreferred embodiments. Other possible variations, modifications, andapplications are also within the scope of the invention. Accordingly,the scope of the invention should not be limited by what has thus farbeen described, but by the appended claims and their legal equivalents.

The invention claimed is:
 1. A beamformer access point comprising: a plurality of antennas; a plurality of radio circuits, each configured to transmit and receive signals via the plurality of antennas, respectively; and a baseband processor configured to monitor signals received by the radio circuits and generate a list of co-channel neighboring beamformee access points, each having a plurality of antennas and located within a clear channel assessment (CCA) range of the beamformer access point, wherein the baseband processor is further configured to cause the radio circuits to transmit via the respective antennas a beamformer sounding sequence to the neighboring beamformee access points on the generated list of co-channel neighboring beamformee access points, according to a multi-user multiple-input-multiple-output (MU-MIMO) air-protocol, and receive from the neighboring beamformee access points Channel State Information (CSI) providing explicit channel estimation information, and wherein the baseband processor of the beamformer access point is further configured to carry out an implicit channel estimation procedure via additional pilot transmissions of the neighboring beamformee access points, appended to the explicit channel estimation information.
 2. The access point according to claim 1, wherein the sounding sequence is based on IEEE802.11ac February 2014 air-protocol, wherein beamformee nodes of the IEEE802.11ac February 2014 air-protocol are the neighboring access points, wherein the CSI is a compressed beamforming message according to the IEEE802.11ac February 2014 air-protocol and is further arranged in a N×M blocks format, at an order that is known to the beamformer access point, and wherein the implicit channel estimation procedure is carried out by receiving from neighboring beamformee access points N pilots, following a transmission of the compressed beamforming message in an order that enables the beamformer access point to map explicit data to implicit measurements.
 3. The access point according to claim 2, wherein the CSI, is ordered in N subgroups, each containing M channel estimation data corresponding to N beamformee and M beamformer antennas, and the implicit channel estimation is acquired by the beamformer access point via the neighboring beamformee access point N pilots, each transmitted through a different one of N antennas thereof, at a same known order in which the CSI N×M blocks were transmitted, so that the beamformer access point maps a given N_(i) received pilot to a N_(i) reported subgroup of the CSI message.
 4. The access point according to claim 2, wherein the beamformer access point is further configured to store the compressed beamforming data in a first N×M memory space residing in the baseband processor, and further configured to receive the N pilots with each of the plurality of M antennas as implicit measurements, and store said received implicit measurements in a second N×M memory space residing in the baseband processor, wherein each entry X_(ij) of the first N×M memory space is mapped to each entry Y_(ij) of the second N×M memory space, based on the known order of transmission.
 5. The access point according to claim 1, wherein the procedure of explicit and implicit sounding processes are performed from time to time and implicit-only sounding is performed before applying a null from one access point to another.
 6. The access point according to claim 4, wherein each entry Y_(ij) is compared to the corresponding entry X_(ij) and a calibration factor Z_(ij) is calculated so that Z_(ij)=Y_(ij)/X_(ij).
 7. The access point according to claim 6, wherein a set of: X_(ij), Y_(ij), and Z_(ij) is stored as a calibration lookup table and wherein implicit sounding measurements Y_(ij) which are carried out without explicit sounding, are corrected by Z_(ij) factor, before applying nulling weighs calculations.
 8. The access point according to claim 7, further configured to access a channel recently being occupied by a downloading listed neighboring access point, via performing channel estimation of the neighboring access point transmission, and applying a receive and a transmit null towards the neighboring access point, wherein the null weights are calculated using the implicit channel estimation, corrected by last stored calibration values Z_(ij).
 9. The access point according to claim 8, wherein the nulling calculated for the neighboring beamformee access point that has recently occupied the channel is performed on the neighboring access point antenna which has recently transmitted a Preamble received by the access point.
 10. The access point according to claim 2, wherein the baseband processor is configured to keep records of previous explicit and implicit sounding processes done per each of the neighboring beamformee access points, and calculate average differences between consecutive explicit reports, as well as average differences between their corresponding implicit channel estimations.
 11. The access point according to claim 8, wherein variations averages, as well as a predicted gradient signs, are considered, as well as time elapsing between two consecutive explicit sounding taking place amongst the access point and each of the listed neighboring access points, in order to calculate a 1^(st) order correction.
 12. The access point according to claim 9, wherein before using the calibration lookup table reference values Z_(ij), the access point uses the parameters to calculate a 1^(st) order correction factor U_(ij), to the Z_(ij) values, so that Z_(ij) ^((′))=Z_(ij)*U_(ij) is used to correct the implicit channel estimation.
 13. The access point according to claim 1, wherein history of explicit sounding is used to gauge channel variation rate, via calculation of average or standard deviation or higher moments of the channel estimation data, and setting thresholds that categorize the mobility level of the access point due to STAs, or objects and people in their area of coverage.
 14. A method for operating a beamformer access point, the method comprising: transmitting and receiving signals via a plurality of antennas and a plurality of radio circuits; monitoring the signals received by the radio circuits and generating a list of neighboring co-channel access points, wherein each neighboring co-channel access point has a plurality of antennas and each is further located within a clear channel assessment (CCA) range of the beamformer access point; instructing the radio circuits to transmit a beamformer sounding sequence to the neighboring access points which are on the list, according to a multi-user multiple-input-multiple-output (MU-MIMO) air-protocol, and receive from the neighboring access points Channel State Information (CSI) which provides explicit channel estimations information, and carry out implicit channel estimations procedure via additional pilots transmissions via the neighboring access points, appended to the explicit channel estimations information.
 15. The method according to claim 14, wherein the sounding sequence is based on IEEE802.11ac February 2014 air-protocol, wherein beamformee nodes of the IEEE802.11ac February 2014 air-protocol are the neighboring access points, wherein the CSI is a compressed beamforming message according to the IEEE802.11ac February 2014 air-protocol and is further arranged in a N×M blocks format, at an order that is known to the receiving beamformer, and wherein the implicit channel estimation procedure is carried out by receiving from neighboring beamformee access points N pilots, following a transmission of the compressed-beamforming in an order that enables the beamformer access point to map explicit data to implicit measurements.
 16. The method according to claim 15, wherein the CSI, is ordered in N subgroups, each containing M channel estimation data corresponding to N beamformee and M beamformer antennas, and the implicit channel estimation is acquired by the beamformer access point via the neighboring beamformee access point N pilots, each transmitted through a different one of N antennas thereof, at a same known order in which the CSI N×M blocks were transmitted, so that the beamformer access point maps a given N_(i) received pilot to a N_(i) reported subgroup of the CSI message.
 17. The method according to claim 15, wherein the beamformer access point is further configured to store the compressed beamforming data in a first N×M memory space residing in the baseband processor, and further configured to receive the N pilots with each of the plurality of M antennas as implicit measurements, and store said received implicit measurements in a second N×M memory space residing in the baseband processor, wherein each entry X_(ij) of the first N×M memory space is mapped to each entry Y_(ij) of the second N×M memory space, based on the known order of transmission.
 18. The method according to claim 14, wherein the procedure of explicit and implicit sounding processes are performed from time to time and implicit-only sounding is performed before applying a null from one access point to another.
 19. The method according to claim 17, wherein each entry Y_(ij) is compared to the corresponding entry X_(ij) and a calibration factor Z_(ij) is calculated so that Z_(ij)=Y_(ij)/X_(ij).
 20. The method according to claim 19, wherein a set of: X_(ij), Y_(ij), and Z_(ij) is stored as a calibration lookup table and wherein implicit sounding measurements Y_(ij) which are carried out without explicit sounding, are corrected by Z_(ij) factor, before applying nulling weighs calculations.
 21. The method according to claim 20, further configured to access a channel recently being occupied by a downloading listed neighboring access point, via performing channel estimation of the neighboring access point transmission, and applying a receive and a transmit null towards the neighboring access point, wherein the null weights are calculated using the implicit channel estimation, corrected by last stored calibration values Z_(ij).
 22. The method according to claim 21, wherein the nulling calculated for the neighboring beamformee access point that has recently occupied the channel is performed on the neighboring access point antenna which has recently transmitted a Preamble received by the access point.
 23. The method according to claim 15, further comprising keeping records of previous explicit and implicit sounding processes done per each of the neighboring beamformee access points, and calculate average differences between consecutive explicit reports, as well as average differences between their corresponding implicit channel estimations.
 24. The method according to claim 21, wherein variations averages, as well as a predicted gradient signs, are considered, as well as time elapsing between two consecutive explicit sounding taking place amongst the access point and each of the listed neighboring access points, in order to calculate a 1^(st) order correction.
 25. The method according to claim 22, wherein before using the calibration lookup table reference values Z_(ij), the access point uses the parameters to calculate a 1^(st) order correction factor U_(ij), to the Z_(ij) values, so that Z_(ij) ^((′))=Z_(ij)*U_(ij) is used to correct the implicit channel estimation.
 26. The method according to claim 14, wherein history of explicit sounding is used to gauge channel variation rate, via calculation of average or standard deviation or higher moments of the channel estimation data, and setting thresholds that categorize the mobility level of the access point due to STAs, or objects and people in their area of coverage. 